1. Field of the Invention
The present invention relates to an adjustable feed block for a coextrusion die, which block is particularly suitable for the continuous production of articles such as thermoplastic profiles which locally possess at least one coating layer such as, for example, a protective layer or a decorative layer.
2. Description of the Background
In the production of extruded articles such as profiles used especially for the production of door frames or window frames, it is desirable to have available profiles which locally possess a surface coating layer providing protection and/or decoration of the profiles. Thus, for example, it is desirable that the face of the profile which subsequently will be required to be exposed to sunlight should be effectively protected by a coating layer containing anti-ultraviolet agents, as is proposed in particular in French Pat. No. 1,571,391. Moreover, it can also be desirable to have available two-coloured profiles which exhibit a particular decorative effect and to achieve this by applying to the surface one or more local coating layers having a different colour from the thermoplastic of which the profile consists.
In order to be able to produce such products it has already been proposed, in Belgian Patent A-805,066, to use an extrusion head equipped with a suitable die, in which the outlet zone of the die is locally equipped with a channel through which the coating layer is delivered, and an adjustment sheet or plate which permits controlling the thickness of the coating layer locally deposited on the extruded profile.
In the device according to the said patent, it is however necessary, for a given profile produced, to change the die and reset the device if, during production, it is desired to alter the location and/or width of the coating layer, and hence it is necessary to clean the die. Moreover, changing to a different type of profile also involves a rather lengthy operation of changing the die and the adjustment. Furthermore, the presence of a thickness-adjusting plate or sheet creates the danger of producing stagnation of molten thermoplastic and hence the danger of thermal degradation of this thermoplastic, especially if it is heat-sensitive. Finally, the equipment required with the device according to the said patent is expensive because it requires having available a series of very elaborate and hence very costly dies.